Rather than start a new thread, I thought I would add my question to this one. I've bought a couple of collections of Kodachromes on eBay, both from the very early 1960's. In one collection the slides have the month and year printed on one corner, Jul 63 and Jul 64 in this case. In the other collection there are no dates on the slides and the only dating evidence I've found is one picture of the Queen visiting Naples, which Google tells me was in May 1961. So my question is, did Kodachrome slides start to have the dates printed on them some time between 1961 and 1963? These were processed in England, if that makes a difference.
My other question is about Kodachromes in grey cardboard mounts with a red border. I have 4 like that in the first collection I mentioned, and I guess they are earlier than the ones in white mounts with the red and yellow Kodak graphic in the corner. What year did that change?